The present invention relates to a method for forming a Group III-V compound semiconductor layer, which is used for a light-emitting element that emits light in a short wavelength range covering violet to ultraviolet wavelengths.
Recently, a light-emitting element for emitting light in the short wavelength range covering the violet to ultraviolet wavelengths is in higher and higher demand as a light source for a next-generation high-density optical disk. Particularly, a Group III-V compound semiconductor layer that contains gallium nitride (GaN) as a main component has been vigorous researched and developed.
A Group III-V compound semiconductor layer, deposited by a metalorganic vapor phase epitaxy (MOVPE) process and containing gallium nitride as a main component, is supposed to have its resistance reduced by introducing a p-type dopant thereto. However, hydrogen atoms bond to the p-type dopant when the layer is passivated with hydrogen, thereby unintentionally deactivating the p-type dopant. For this reason, it is difficult to reduce the resistance of the p-type Group III-V compound semiconductor layer.
In view of this, a countermeasure process was proposed in Japanese Laid-Open Publication No. 5-183189. Specifically, in this process a p-type gallium nitride semiconductor layer is deposited on a substrate and then annealed at a temperature of 500° C. or more in an ambient containing substantially no hydrogen, thereby ejecting hydrogen from the p-type gallium nitride semiconductor layer and activating the p-type dopant. In this manner, the p-type gallium nitride semiconductor layer should have its resistance reduced.
Further, as described in Japanese Laid-Open Publication No. 5-183189, if the p-type gallium nitride semiconductor layer is annealed in this manner, the resistivity of the p-type gallium nitride semiconductor layer can be reduced to somewhere between 1×106 Ω·cm and several Ω·cm.
However, the present inventors were confronted with a fact that it was impossible to reduce the resistivity of the p-type gallium nitride semiconductor layer to about 1×106 Ω·cm to several Ω·cm as intended even if the p-type gallium nitride semiconductor layer was annealed at a temperature of 500° C. or more in an ambient containing substantially no hydrogen.